U.S. Pat. No. 6,986,812 of Dubey et al., incorporated herein by reference in its entirety, features a slurry feed apparatus for use in a SCP panel production line or the like application where settable slurries are used in the production of building panels or board. The apparatus includes a main metering roll and a companion roll placed in close, generally parallel relationship to each other to form a nip in which a supply of slurry is retained. Both rolls preferably rotate in the same direction so that slurry is drawn from the nip over the metering roll to be deposited upon a moving web of the SCP panel production line. A thickness control roll is provided in close operational proximity to the main metering roll for maintaining a desired thickness of the slurry.
U.S. Pat. No. 7,524,386 B2 to George et al, incorporated herein by reference in its entirety, discloses a process employing a wet mixer having a vertical mixing chamber for forming a wet slurry of a cementitious powder and liquid. The vertical mixing chamber is designed to provide the required amount of mixing to provide thoroughly mixed, uniformly thin slurry within a mixing residence time that allows for adequate supply of slurry to ensure continuous operation of an associated cement panel production line. Gravity feed means for supply of cementitious powder and water to the slurry mixing area of the chamber is also disclosed. In preparing the SCP panels, an important step is mixing cementitious powder to form slurry. The slurry is then withdrawn from the bottom of the chamber and pumped through a cavity pump to the slurry feeding apparatus. A typical conventional continuous cement mixer is the DUO MIX2000 continuous cement mixer from M-TEC GmbH, Neuenburg, Germany which is used in the construction industry to mix and pump concrete slurry.
U.S. Pat. No. 7,513,963 B2 to George et al, incorporated herein by reference in its entirety, discloses a wet mixer apparatus and method for its use, the mixer having a vertical mixing chamber for forming a wet slurry of a cementitious slurry and water. The vertical mixing chamber is designed to provide the required amount of mixing to provide thoroughly mixed, uniformly thin slurry within a mixing residence time that allows for adequate supply of slurry to ensure continuous operation of an associated cement panel production line. Gravity feeding for separate supply of cementitious powder and water to the slurry mixing area of the chamber without pre-mixing of the powder and water is also disclosed.
U.S. Pat. No. 8,038,790 to Dubey et al., incorporated herein by reference in its entirety, discloses structural cement panel for resisting transverse and shear loads equal to transverse and shear loads provided by plywood and oriented strain board, when fastened to framing for use in shear walls, flooring and roofing systems. The panels provide reduced thermal transmission compared to other structural cement panels. The panels employ one or more layers of a continuous phase resulting from curing an aqueous mixture of calcium sulfate alpha hemihydrate, hydraulic cement, coated expanded perlite particles filler, optional additional fillers, active pozzolan and lime. The coated perlite has a particle size of 1-500 microns, a median diameter of 20-150 microns, and an effective particle density (specific gravity) of less than 0.50 g/cc. The panels are reinforced with fibers, for example alkali-resistant glass fibers.
US Patent Application Publication No. 2005/0064164 to Dubey et al., incorporated herein by reference in its entirety, discloses a multi-layer process for producing structural cementitious panel which includes: (a.) providing a moving web; (b.) one of (i) depositing a first layer of individual, loose fibers upon the web, followed by depositing a layer of settable slurry upon the web and (ii) depositing a layer of settable slurry upon the web; (c.) depositing a second layer of individual, loose fibers upon the slurry; (d.) actively embedding said second layer of individual, loose fibers into the slurry to distribute said fibers throughout the slurry; and (e.) repeating steps (ii) through (d.) until the desired number of layers of settable fiber-enhanced slurry is obtained and so that the fibers are distributed throughout the panel. Also provided are a structural panel produced by the process, an apparatus suitable for producing structural cementitious panels according to the process, and a structural cementitious panel having multiple layers, each layer created by depositing a layer of settable slurry upon a moving web, depositing fibers upon the slurry and embedding the fibers into the slurry such that each layer is integrally formed with the adjacent layers.
US Patent Application Publication No. 2006/0061007 to Chen discloses a method and apparatus for extruding cementitious articles. The extruder includes a casing with a pair of inter-meshing self-wiping screws rotatably mounted therein. The screws continuously mix and knead the components of the fiber cement provided through various feed means to form a substantially homogeneous paste and force the paste through a die to form a green cementitious extrudate suitable for casting. Cementitious mixtures for extruding are very viscous and not suitable for uses such as shotcrete or deposition through a headbox on a cementitious panel production line.
The current state-of-the-art mixing technology for producing fiber reinforced cementitious slurry typically involves use of industry standard batch mixers into which all raw materials including reinforcing fibers are first added and then mixed for several minutes to yield a slurry mixture with randomly dispersed fibers. Rotating drum and rotating pan mixers are examples of concrete mixers that are commonly used for preparing fiber reinforced cementitious slurry mixtures. Some major limitations and drawbacks of the current state-of-the art concrete mixers and mixing technologies for producing fiber reinforced cementitious slurry mixtures include:
The mixing operation in a batch mixer is not continuous thus making their use more difficult in applications where a continuous supply of slurry is needed such as in the case of a continuous panel production line.
The mixing time in a batch mixer is typically very long, in the order of several minutes, to obtain a well-blended, homogeneous slurry mixture.
Since a large amount of fibers are added at a time in a batch mixer, that leads to fiber lumping and balling during the mixing operation.
Longer mixing times involved with the batch mixing process tend to damage and break the reinforcing fibers.
Batch mixers are not very useful and practical with respect to handling rapid setting cementitious materials.
There is a need for a single-layer process for producing slurry for cementitious panels having high reinforcing fiber concentrations. Thus, there is a need for an improved wet mixing apparatus that ensures supply of sufficient mixed fluid cementitious slurry which contains glass fibers to supply a continuous panel production line. It is desired to provide a degree of mixing of the cementitious reactive powder, glass fibers, and water in the mixer to result in a slurry of proper rheology and sufficient fluidity to provide a slurry for use in the continuous cementitious panel manufacturing line.